In the BlackBerry Administration Service, on the BlackBerry solution management menu, expand User.
Click Manage users.
Search for the user account.
In the search results, click the name of the user account.
Click Edit user.
In the Messaging configuration section, click Default configuration.

when I click on the default configuration is very very slow, after some time page expires.

Default Configuration for a user is a collection sets of configurations that have to be read from the database. Is your SQL server that host the BESMgmt database have latency issue with the computer that runs the BAS?

Check the snip from KB24632 below:-

"To maximize the performance of the BlackBerry Administration Service and avoid slow response times, computers that host the BlackBerry Administration Service should be placed in the same data center as the Microsoft® SQL Server® that hosts the BlackBerry Configuration Database. Round-trip latency should be less than 20 milliseconds."